In small dynamoelectric machines, such as fractional horsepower electric motors, it is conventional to journal a rotating shaft in one or more sleeve-type bearings of a bearing assembly. Besides the sleeve-type bearings, such bearing assemblies conventionally include a lubricant reservoir containing an absorbent material such as wool felt or extrudable material of the type disclosed in Whitt U.S. Pat. No. 3,894,956, means such as a felt wick for depositing a film of lubricant on the shaft within the sleeve-type bearing and means for recirculating the lubricant which escapes along the bearing journal back to the reservoir for reuse. Such a lubricant supply and recirculation apparatus is shown, for example, in Cunningham U.S. Pat. No. 3,885,176. Stokke et al. U.S. Pat. No. 3,793,543 defines the parameters of a lubricant recirculation system to minimize loss of lubricant from the system.
For many applications, it is desirable that the bearing assembly be tolerant of angular misalignment of the shaft and the sleeve-type bearing. In Shaffer et al. U.S. Pat. No. 3,164,422, a sleeve-type bearing is formed with a generally hemispherical outer surface at one end thereof which is adapted to be assembled into a similarly shaped concavity in an end cover of a dynamoelectric machine. The Shaffer et al. device employs a large number of parts. The large number of parts increases assembly labor and the necessity to assemble the bearing assembly into the end cover of the dynamoelectric machine prevents efficient subassembly of the bearing assembly for later insertion into the dynamoelectric machine.
A shaft rotating in a sleeve-type bearing theoretically touches the bearing only along a line of contact which is determined by the direction of load application and the direction of shaft rotation. When a lubricant such as oil is introduced into the sleeve-type bearing it tends to separate the rotating shaft from the stationary bearing sleeve. At some value of shaft speed, dependent on bearing area, lubricant temperature and applied load, conveniently, for example, at a speed of 900 rpm, the lubricant develops a hydrodynamic film upon which the rotating shaft is supported away from the bearing sleeve.
In a self-aligning bearing, the bearing sleeve must be left free for angular adjustment. This freedom is provided in the Shaffer et al. patent, for example, by sliding contact between the hemispherical end surface of the bearing sleeve and the mating shape in the end cover of the dynamoelectric machine as well as by leaving the other end of the bearing sleeve without rigid contact with the structure. Such contact over only part of the surface of a bearing sleeve is less effective for conducting heat from the bearing than is the more usual intimate contact achieved by press fitting or integral manufacture. There is thus a tendency for the lubricant temperature to be higher in such a self-aligning bearing. If the lubricant temperature becomes too high, the hydrodynamic film set up by the rotating shaft may break down to thus permit the generation of additional heat. If this happens, the additional heat further interferes with adequate lubrication and this process can continue until the equipment fails.